Configuring Time Synchronization in Active Directory: NT5DS and NTP

Accurate time synchronization is important in any network, especially in Active Directory environments, where slight discrepancies in time can lead to authentication failures, logging discrepancies, and various other issues.

Windows domains utilize the Windows Time Service (W32Time) to ensure that all members of the domain are using the same clock source. This short article explains the two primary time synchronization hierarchies used in Active Directory: NT5DS and NTP, and provides guidance on configuring them.

Understanding NT5DS and NTP

• NT5DS: This mode leverages the domain hierarchy for time synchronization. The primary domain controller (PDC) emulator of the root domain becomes the authoritative time source for all other domain controllers and member computers. This is the default setting for Windows domain-joined computers.

• NTP (Network Time Protocol): This mode is used for direct synchronization with a specified NTP server. It's typically used for standalone computers or when you need to synchronize with an external time source.

Configuring NT5DS in Active Directory

1. Identify the PDC Emulator: The PDC emulator in the root domain should synchronize with a reliable external time source. Use the command to identify the PDC emulator:

   netdom query fsmo

2. Configure External Time Source on the PDC Emulator:

   • Open Command Prompt as Administrator.

   • Run the following command, replacing <NTPServers> with your chosen NTP server(s):

     w32tm /config /manualpeerlist:"<NTPServers>" /syncfromflags:manual /reliable:YES /update

   • Restart the time service with:

     net stop w32time && net start w32time

Configuring NTP Mode

Use NTP mode for computers that are not part of a domain or when specific devices need to synchronize with a different time source:

1. Open Command Prompt as Administrator.

2. Configure the NTP Client by running the following command, again replacing <NTPServers> with your chosen NTP server(s):

   w32tm /config /syncfromflags:manual /manualpeerlist:"<NTPServers>" /reliable:NO /update

3. Restart the Time Service with:

   net stop w32time && net start w32time

Verifying Configuration

After configuring time synchronization, verify that your settings are effective:

• Check the current configuration with:

  w32tm /query /configuration

• View the status of the time service and confirm it's synchronizing correctly with:

  w32tm /query /status

Best Practices

• Always configure the PDC emulator in the root domain to synchronize with an external, reliable time source.

• Ensure all domain controllers synchronize time with their parent domain PDC emulator.

• Use NTP mode primarily for systems that require specific time synchronization needs outside the domain hierarchy.